1. Field of the Invention
The present invention relates to an automatic tuning apparatus, and more particularly, it relates to an automatic tuning apparatus for a VTR, which is adapted to discriminate the signal system and process stored signal information in automatic tuning.
2. Description of the Background Art
A conventional automatic tuning apparatus for a VTR (video tape recorder) is now described with reference to FIGS. 51 to 53. FIG. 51 is a block diagram showing a principal part in the conventional automatic tuning apparatus for a VTR, and FIG. 52 is a flow chart as to its operation. FIG. 53 shows the relations between station numbers (expedient broadcasting station numbers) and position numbers (expedient numbers on the VTR unit for selecting the broadcasting stations) after completion of tuning.
Referring to FIG. 51, numeral 2 denotes a tuner circuit which can be switched in correspondence to a video signal system by an external control signal, numeral 3 denotes a video signal processing circuit (referred to as Y/C in the figure) including a synchronizing signal (abbreviated as SYNC) separation circuit which receives a composite video signal S1 from the tuner circuit 2 and carries out signal processing, numeral 4 denotes an AFT detection circuit which detects presence/absence of a broadcasting station by a signal received from the tuner circuit 2, numeral 5 denotes a tuning control circuit, and numeral 6 denotes a memory circuit, and a system controller 7 is formed by the tuning control circuit 5 and the memory circuit 6. Numeral 8 denotes an input signal system switch for switching the operation of the tuning control circuit 5 in response to the carrier system of the input signal.
The operation is now described with reference to FIGS. 52 and 53. First, the operation of automatic tuning (hereinafter referred to as auto tuning) is described with reference to the flow chart of FIG. 52. When a command for automatic tuning (hereinafter referred to as auto tuning) is received from the user, the system controller 7 sets the tuning mode of the tuner circuit 2 at the PAL system and sets a memory address of the memory 6 at a station number "0", as initialization (step ST1).
Then, a tuning control signal S3 is transmitted to the tuner circuit 2, to control the same in a direction for increasing its tuning frequency by a constant amount (step ST2).
At this time, an AFT (automatic fine tuning) signal S4 which is outputted from the AFT detection circuit 4 and a SYNC signal S2 indicating presence/absence of a signal separated by the video signal processing circuit 3 are inputted in the tuning control 5 for making a discrimination, in order to detect presence/absence of a broadcasting station transmitting a signal of the frequency (step ST3).
When both of the AFT signal S4 and the SYNC signal S3 are supplied at this point of time, the tuning control circuit 5 determines that it has been possible to receive the signal from the broadcasting station, and stores current tuning data in the address of the station number "0" in the memory 6 (step ST4). The tuning data indicates data related to the frequency.
Then, the address of the memory 6 is incremented by one to a station number "1" to enter a next tuning operation, in order to store next tuning data (step ST5).
When both of the AFT signal S4 and the SYNC signal S2 are not supplied, on the other hand, a discrimination is made as to whether or not the current frequency reaches the upper limit of the tuning frequency, i.e., whether or not the tuning is ended (step ST6). The tuning is ended if the current frequency reaches the upper limit of the tuning frequency, otherwise the operation at the step ST2 is carried out again. The operations at the steps ST2 to ST6 are repeated, so that the tuning is ended when the frequency reaches the upper limit of the tuning frequency.
The tuning data obtained by the tuning is supplied to a channel selection system from the address in the memory 6, so that a position number for channel selection is allotted and the tuning mode is ended.
Results obtained by the aforementioned auto tuning are expressed as shown in FIG. 53. FIG. 53 shows station numbers of the addresses of the memory 6 and the tuning data stored therein, and the relations between the station numbers and the position numbers for channel selection.
FIG. 53 indicates that frequency data corresponding to transmission frequencies of "B station", "D station", "C station" and "A station" are stored in the station numbers "0" to "3" as the tuning data respectively. On the other hand, it indicates that no data to be stored are present, i.e., no broadcasting stations are present in the station numbers "4" to "99".
In the channel selection system, the frequency data corresponding to the transmission frequencies of "B station", "D station", "C station" and "A station" are stored in the position numbers "0" to "3" respectively, while the position numbers "4" to "99" are skipped since no data reading is necessary.
The user can use the channel selection system of the VTR from the point of time when the auto tuning is completed, and obtain a tuned signal by selecting a switch corresponding to the position number. In the auto tuning, the tuning operation is carried out only as to a signal which is transmitted in the PAL system, and hence no signal transmitted in a transmission system other than the PAL system can be obtained. In order to tune a signal of a transmission system other than the PAL system, the input signal system switch 8 which is connected to the tuning control circuit 5 is so switched that the tuning control circuit 5 supplies a control signal SCON for switching the input signal system to the tuner circuit 2.
The conventional automatic tuning apparatus is structured in the aforementioned manner, and hence the transmission system of the input signal is set at the PAL system in initialization. In order to tune a signal of a transmission system other than the PAL system, the user must manually switch the input signal system switch 8 after completion of auto tuning, to carry out re-tuning.
In the auto tuning, further, only the data related to the frequency is stored and hence there are no data as to the type of the tuned broadcasting station, strongness/weakness of the signal, and the sound and video signal systems which are varied with countries. Thus, the user is disadvantageously forced to select the position in relation to these differences after completion of the auto tuning.